The present invention relates generally to systems and methods for analyzing the viscoelastic properties of combinatorial libraries of materials. More specifically, the present invention relates to systems and methods for analyzing the thermal properties of libraries of polymers and polymer films using an array of full bridge devices. The systems and methods of the present invention may also be used to analyze such properties as vapor sorption, chemical resistance, weatherability, and oxidative stability.
Typically, the viscoelastic properties of materials, such as polymers and polymer films, have been analyzed using devices such as acoustic wave devices, micro-hotplates, micromechanical calorimetric sensors, and shear/stress sensors. For example, acoustic wave devices have been used to measure the glass transition temperature and melting temperature of materials. Micro-hotplates have been used as micron-scale differential scanning calorimeters on a chip. Micromechanical calorimetric sensors have been used to detect thermal changes in test samples containing biomolecules undergoing chemical and biochemical reactions. Other sensor devices have been arranged in a standard combinatorial array configuration.
U.S. Pat. No. 4,312,228 discloses an acoustic wave sensor and methods for monitoring predetermined parameters of polymers including generating a surface acoustic wave in a piezoelectric material element and contacting a thin layer of the polymer with the surface through which the acoustic wave travels. The thin polymer layer is subjected to variations in environment thereby modifying the predetermined parameter of the polymer and changing the velocity of acoustic waves in and/or a dielectric property of the polymer, thus altering the frequency, amplitude, and/or phase of the surface acoustic wave. These alterations may be measured and related to glass transition temperature, the rate of solvent evaporation from the polymer, the photo-crosslinking characteristics of the polymer, and the crystalline transition characteristics of the polymer.
U.S. Pat. No. 6,079,873 discloses a differential scanning microcalorimeter produced on a silicon chip that enables microscopic scanning calorimetry measurements of small material samples and thin films. The microcalorimeter includes a reference zone and a sample zone. An integrated polysilicon heater provides heat to each zone and a thermopile including a succession of thermocouple junctions generates a voltage representing the temperature difference between the reference zone and the sample zone. Temperature differences between the zones provide information about the chemical reactions and phase transitions which occur in a sample placed in the sample zone.
U.S. Pat. No. 5,451,371 discloses a non-scanning, constant temperature microcalorimeter device. The device is built on a silicon base which is etched, leaving a frame of silicon supporting two polysilicon platforms. A catalyst is disposed on one platform to sense the presence of hydrocarbons. Platinum resistors on each platform serve as heaters and thermometers.
U.S. Pat. No. 6,096,559 discloses a calorimeter sensor apparatus using microcantilevered spring elements for detecting thermodynamic changes within a material sample containing biomolecules that undergo chemical and biochemical reactions. The spring elements each include a bimaterial layer of chemicals disposed on a coated region of at least one surface of the microcantilever. The chemicals generate a differential thermal stress across the surface upon reaction of the chemicals with an analyte or biomolecules within the sample due to the heat of the resulting reactions. The thermal stress experienced by the spring element creates a mechanical bending of the microcantilever. Deflections of the microcantilever may be detected by a variety of detection techniques.
U.S. Pat. No. 5,719,324 discloses a piezoelectric transducer that is fabricated with a cantilever having a spring element which is treated with a chemical having an affinity for a specific vapor phase chemical. An oscillator means maintains a resonant vibrational frequency during the detection of the chemical, with changes in resonant vibrational frequency indicating amounts of the targeted chemical present in the monitored atmosphere.
U.S. Pat. No. 5,445,008 discloses a mass microsensor that is also fabricated with a microcantilever having a material which absorbs a targeted chemical from the monitored atmosphere. Oscillation is induced using a piezoelectric transducer and the resonant frequency of the microcantilever is analyzed to detect amounts of the targeted chemical present in the monitored atmosphere. U.S. Pat. No. 5,475,318 discloses a microprobe including a microcantilever, a base, a probe tip projecting from the base, and a heating element that may be used to probe the material to be investigated.
U.S. Pat. No. 4,963,815 discloses a device and a method for determining an analyte by measuring a redox potential-modulated photoinducing electrical signal from an electrically conducting layer of a semiconductor device.
U.S. Pat. No. 6,106,149 discloses a mass and heat flow measurement sensor including a microresonator, such as a quartz crystal microbalance (QCM), a heat flow sensor, such as an isothermal heat conduction calorimeter, and a heat sink thermally coupled to the heat flow sensor. The microresonator may be used to measure changes in mass of a material sample at its surface and the heat flow sensor, which is thermally coupled to the microresonator, may be used to measure heat flow from the material sample to the heat sink.
U.S. Pat. No. 6,157,009 discloses a reactive screening tool, such as a calorimeter apparatus, having a low test cell-to-test sample thermal mass ratio so as to minimize heat sink effects on the test sample during chemical reaction. A heater control algorithm includes a calibration stage during which the heater is set to the predetermined test conditions and a test stage during which the heater controls the test conditions in a ramping mode and in an adiabatic mode. The reactive screening tool may also include a foam detector for detecting the presence of foam in the test sample.
U.S. Pat. No. 5,563,341 discloses a vapor pressure sensor including a substrate having a body with first and second parallel planar surfaces. A hole is formed in the body and extends through and between the first and second surfaces. A beam disposed within the hole in the body is formed as a cantilever. A vapor absorbing polyimide coating of substantially uniform thickness is disposed on the surface of the beam in full shear restraint. A strain measuring device forms a portion of a bridge carried by the substrate and measures shear forces exerted on the beam by the vapor absorbing coating.
U.S. Pat. No. 4,969,359 discloses a silicon accelerometer responsive to three (3) orthogonal force components. Three rectangular beams or cantilevers are formed, each having vertical sidewalls lying in crystalline planes orthogonal to one another.
U.S. Pat. No. 6,126,311 discloses a dew point sensor using micro-electromechanical systems (MEMS) including a microcantilevered beam formed on a substrate. A cooling device and a temperature sensor are in thermal communication with the microcantilevered beam and a control circuit operable for controlling and monitoring its resonance. The dew point is determined by identifying the temperature of the microcantilevered beam when its resonance or vibratory mode changes due to a change in mass caused by the formation of dew on the microcantilevered beam.
U.S. Pat. No. 6,016,686 discloses a micromechanical microcantilever potentiometric sensor used for detecting and measuring predetermined physical and chemical parameters in a material sample. A spring element includes a region coated with at least one chemical coating that accumulates a surface charge in response to hydrogen ions, redox potential, or ion concentrations in the material sample being monitored. Differing surface charges on opposing surfaces create a mechanical stress and a deformation of the spring element. A multitude of detection methods may be used to measure the deflection of the spring element and the degree of deflection may be correlated with the physical or chemical parameter of interest.
U.S. Pat. No. 6,269,685 discloses a method for the measurement of the viscosity of a fluid that uses a micromachined cantilever mounted on a moveable base. As the base is rastered while in contact with the fluid, the deflection of the cantilever is measured and the viscosity of the fluid is determined by comparison with standards. U.S. Pat. No. 5,130,257 discloses a viscosity sensor fabricated using a surface transverse wave device. Similarly, U.S. Pat. No. 5,494,639 discloses a disposable biosensor that uses a vibrating member disposed beneath a cell operable for measuring blood coagulation time as a function of viscosity.
U.S. Pat. No. 6,167,748 discloses a multi-element sensor array with common-mode cancellation and a multi-element apparatus for detecting the presence of at least one chemical, biological, or physical component in a monitored area. The array includes a capacitive transducer having at least one cantilever spring element coated with a chemical having an affinity for the component to be detected, a pick-up plate, and detection means for measuring the variation in capacitance between the cantilever spring element and the pick-up plate, forming a measurement channel signal.
U.S. Pat. No. 6,289,717 discloses a micromechanical antibody sensor using a microcantilevered spring element having a detector molecule coating, such as an antibody or antigen coating. A material sample containing a target molecule or substrate is introduced to the coating. The spring element measurably bends in response to the stress induced by the binding that occurs between the detector molecules and the target molecules.
Such systems and methods, although marginally useful, suffer from several important limitations when used to analyze the viscoelastic properties of combinatorial libraries of materials, such as libraries of polymers and polymer films. The operation of an array of sensors in the screening of combinatorial libraries of materials is typically unacceptably slow. Measurements are typically performed in a serial fashion and the screening of as few as 100 combinatorial materials may take in excess of 90 minutes. The electronics used to operate such arrays of sensors are also complex and expensive. For example, a lock-in amplifier is typically required. Finally, the use of shear/stress sensors as true microcalorimeters in the analysis of the thermal properties of combinatorial libraries of materials is limited because such sensors typically do not have individual heaters associated with them. Thus, the use of such sensors in the thermal analysis of combinatorial libraries materials requires the use of separate heaters and temperature sensors, and a complete modification of the sensor elements. Thus, what is needed are systems and methods that provide improved capabilities for the analysis of the thermal properties of combinatorial libraries of materials, such as libraries of polymers and polymer films. What is needed are systems and methods that allow for the simultaneous and continuous measurement, with high sensitivity and accuracy, of the viscoelastic changes in a plurality of low volume material samples, such as those generated in combinatorial chemistry experiments. Furthermore, due to the large number of samples involved in a typical combinatorial chemistry experiment, automated computational methods for the detection of outliers and the determination of viscoelastic properties are needed.
The present invention provides systems and methods having improved capabilities for the analysis of the viscoelastic properties of combinatorial libraries of materials, such as libraries of polymers and polymer films. These systems and methods include the use of an array of miniaturized shear/stress devices, or full bridge devices, that operate in parallel, providing simultaneous and continuous responses. The sensor data may be read electronically and is used an input for multivariate statistical algorithms providing data extraction and compression for automated outlier detection and improved analysis.
In one embodiment, a system for analyzing a viscoelastic property of combinatorial materials includes a plurality of full bridge devices operable for measuring an environment-modulated elongation property of the combinatorial materials, wherein each of the plurality of full bridge devices comprises a plurality of strain gauges operable for measuring an environment-modulated elongation property of the combinatorial materials, and wherein each combinatorial material is disposed on a surface of the plurality of full bridge devices. The system also includes a mathematical algorithm disposed within a computer, the mathematical algorithm operable for equating the environment-modulated elongation property of the combinatorial materials with a viscoelastic property of the combinatorial materials.
In another embodiment, a method for analyzing a viscoelastic property of combinatorial materials includes providing a plurality of full bridge devices operable for measuring an environment-modulated elongation property of the combinatorial materials, wherein each of the plurality of full bridge devices comprises a plurality of strain gauges operable for measuring the environment-modulated elongation property of the combinatorial materials, disposing the combinatorial materials on a surface of the plurality of full bridge devices, and measuring the environment-modulated elongation property of each combinatorial material. The method also includes providing a mathematical algorithm operable for equating the environment-modulated elongation property of the combinatorial materials with a viscoelastic property of the combinatorial materials and equating the environment-modulated elongation property of the combinatorial materials with a viscoelastic property of the combinatorial materials.
Advantageously, the present invention provides systems and methods that use a plurality of strain gauges and the temperature-modulated elongation properties of a polymer or polymer film to characterize the thermal properties of the polymer or polymer film. These systems and methods are capable of measuring the thermal properties of any combinatorial material that may be deposited onto a substrate and that experiences stress when a member held in full shear restraint is subjected to varying thermal or other conditions. These systems and methods allow for the mass-independent characterization of polymers and polymer films using a miniaturized, inexpensive, mass-produced device. Finally, the systems and methods of the present invention allow for the simultaneous and continuous measurement of signals produced by a plurality of individual devices, allowing for the simultaneous and continuous analysis of data using multivariate statistical data analysis techniques and visualization algorithms.